PVDF based coatings (or "paints") have been used and are known to be very good protective coatings for various substrates. They have excellent resistance to weathering and chemical attack.
The traditional method for preparing PVDF based paint has been to formulate a liquid dispersion coating. The liquid vehicle has traditionally been a solvent, but increased environmental laws and regulations have made it more difficult and costly to handle and recover such solvents. Thus, there is a need for solvent-less PVDF based coating systems.
PVDF based powder coatings have traditionally exhibited a certain amount of surface roughness, commonly known as "Orange Peel." This undesirable Orange Peel surface has affected the market acceptance of PVDF based powder coatings as a viable alternative to the liquid, solvent based PVDF coatings.
There are a number of ways which have been tried to reduce the amount of Orange Peel. One is to reduce the melt viscosity of the PVDF resin, but this generally has an adverse effect on the mechanical properties of the coating, such as resistance to impact and flexibility. Another approach, disclosed in European Patent Application 284,996, is to use a coalescing additive which is substantially volatilized from the coating during coalescence; this, however, again introduces the problem of release of solvents. Still another alternative proposed in U.S. Pat. No. 4,770,939 is the incorporation of an acrylic flow modifier, but this is described by the patentee as "not essential."